1. Field of the Invention
The present invention relates to methods and apparatus for avoiding the occurrence of moire in color scanners for graphic art.
2. Description of the Prior Art
It is known that when a color separation film is produced by a color scanner, unwanted moire patterns (hereinbelow referred to merely as moire) are produced. The causes are presumably as follows:
(1) Interference between light patterns of the pattern images and of the screen net;
(2) Interference between light patterns of the pattern images and the scanning lines; and/or
(3) Interference between light patterns of the patterns in the color original and those provided by apertures on the pick-up of the scanner.
The unwanted moire appears particularly when the color original contains repeated pattern designs, such as fabric texture and arranged bricks in buildings, wherein it appears as color diffusion in the form of new patterns not present in the original.
A color separation film having moire must be discarded as a defective product, which leads to an economic loss.
In order to avoid the occurrence of moire in color scanning, one solution is to change the diameters of the apertures of the pick-up in accordance with the mode of representation of the patterns in the color original. Another solution is to image out of focus deliberately so as to scan the images within an allowable limit for out-of-focus.
However, these solutions require experience and skill for the operator, and are not suitable for the inexperienced operators. In addition, a stabilized color separation film is difficult to obtain. Furthermore, it is impossible to avoid the occurrence of moire beforehand, thereby allowing moire to appear on the film.